Process for the demetallization of petroleum residuums



M1t.)'l2,1970A Y R. a. LONG ETAL 3,511,774

' PROCESS FOR THE DEMETALLIZATION OF PETROLEUM RESIDUMS Filed Jan. 25. 1968 H. J. SOLOMON Inventors Patent Attorney i United States Patent O ice 3,511,774 PROCESS FOR THE DEMETALLIZATION OF i PETROLEUM RESIDUUMS ABSTRACT 0F THE DISCLOSURE A.process foil' the demetallization of a petroleum residuum fraction wherein the asphalt is contacted with a polar solvent at a (CT-l) of 5-50" F. above the critical temperature of the solvent and a (CP-|) pressure of 3D0-1000 p.s.i.g. above the critical pressure of the solvent.

Petroleum residuum fractions are demetallized in a multistage separation processcomprising conventional deasphalting followed by additional separation with a polar solvent at supercritical conditions.

v It. is well known that organometallic compounds in petroleum fractions tend to poison petroleum refining catalysts employed in continuous operations. It is also well known that it is desirable to avoid high metal contents in fuel oils because metals cause corrosion and other problems when fuels are burned in industrial furnaces.

Certain petroleum residuum fractions have a metals content of over about 200 p.p.m. Conventional propane deasphalting can be used to' separate an extract fraction containing about 5-100 p.p.m. metals which is a suitable material for treatment and conversion in the presence of catalysts. However, propane deasphalting is limited in that 1twill extract only about 40-60% of a petroleum residuum and the bottoms fraction amounting to about ilal of] theresiduum is unsuitable for use except as heavy The object of the process of this invention is to provide an additional quantity of oil having an intermediate quantity of metals that canA be used in a number of ways which will be described below. A

Briey summarizing, the process comprises the steps of subjecting a residuum to conventional deasphalting, passing the asphalt to a supercritical separation unit, contacting the asphalt with a polar solvent atsupercritical conditions and recovering demetallized fractions.

Further details of the invention will be disclosed with reference tov the drawing which discloses a preferred embodiment of the invention.

3,511,774 Patented May 12, 1970 Any number of fractions can be recovered from the distillation zone for further refining. A bottoms fraction or petroleum residuum having an initial boiling' "point in the range of 500-1000 F. islremoved by line 4 and passed to a conventional deasphalting tower 5. If desired, the distillation bottoms can' be blended with other heavy fractions derived from petroleum refining operations. Generally speaking, from 30-90% of the material in linev 4 boils above 900 F. The material will have av gravity of 525 API, a sulfur content of 1-8 wt. percent, a Conradson carbon of 5 25 wt. percent and a metals content of -2000 p.p.m. The metals include vanadium, nickel, copper, iron and others.

Deasphalting is carried out in the conventional manner employing a non-polar light aliphatic hydrocarbon solvent containing 3 to 8 carbon atoms in the molecule. Specifically, propane, butane, pentane, hexane or mixtures thereof are used. When propane is used-as the solvent, conditions in tower 5 include a temperature in the range'of 120 to F., a pressure in the range of 500 to 900 p.s.i.g. and a solvent to oil ratio of 0.5 to 8.0. Deasphalted oil and solvent are passed overhead by line 6, cooled in cooler 7 and fed into ilash drum 8. PropaneV is ilashed overhead and recycled via line 9, cooler 10 and pump 11 to tower 5. A low metals oil containing less than about 100 p.p.m. metals, preferably less than about 50 p.p.m. metals, is recovered `by line 12. This oil may be subjected to catalytic hydrodesulfurization since the metals content is now below the quantity of metals which causes rapid poisoning of hydrodesulfurization` catalysts such as cobalt molybdate on alumina.

The bottoms or raffinate from the deasphalter is passed by line 13 containing pump 14 to supercritical separation unit (SCS Unit) 15.

In supercritical separation, the separation of the fraction(s) is primarily by molecular weight of the components and this is similar to distillation. In addition some influences of compound type are evident resulting in separation effects like those of solvent extraction.

A requirement of supercritical separation is that at least two phases must be formed by the solvent-feed mixture. If the properties of the feed are too similar to those of the solvent, the mutual solubility of thetwo will be so great that the formation of two phases will be impossible. Generally, it is preferred that the initial boiling point of the feed should be about 200 F. above the critical temperature of the solvent.

The mode of operation of supercritical separation and the processing equipment used are similar to those used in solvent extraction. In one embodiment, the solvent or carrier gas is mixed with the fraction or oil-solid slurry to be separated at supercritical conditions and two fluid phases are formed. In a preferred embodiment shown in the drawings of this disclosure the feed and solvent are passed through a countercurrent contacting tower at supercritical conditions. This unit may be either `single stage or multistage. A light oil phase containing an intermediate quantity of metals is recovered overhead and a high metals asphalt phase is recovered as bottoms. The solvent is recovered from the separated fractions and recycled. The tower can have shed trays, rotating disc mixers, disc and donut trays, or the like as internals. In multistage peration, reilux may also be desirable. In addition, the :parationmay be carried out in a conventional mixerlttler type of contactor.

The most important operating variable in supercritical :paration is temperature. It is necessary to operate at a mperature signilcantly above the critical temperature the solvent in order to obtain the improved selectivity laracteristics of this process. This operating temperare shall sometimes hereinafter be referred to as CT+, e. critical temperature plus. For any particular feed ld solvent there isla narrow optimum CT+ range which illl provide the desired enhanced selectivity. If the opering temperature is below the optimum range, selectivity not improved. If thetemperature is above the optimum nge, the yield of the light phase is decreased. Pressure is also an important operating variable. The paclty of va. solvent or a carrier gas to extract a light l phase from an asphaltic feed is essentially nil at essures below the critical pressure of the solvent. This pacrty increases with increasing pressure. This operateI g pressure shall sometimes hereinafter be referred to as Pfl@ 1.e. critical pressure plus. The optimum upper mt of operating pressure is not so sensitive or narrow terms of decline in selectivity as itis in the case of the per temperature limitation. Instead, equipment limitans such as wall thickness of reactors, separators and ning alect the selection of operating pressure. The light phase taken overhead from the supercritical poration zone comprises a mixture of solvent and light at' supercritical conditions. The oil can be recovered m the solvent by either increasing the temperature or decreasing the pressure on the light phase or both nultaneously. If desired, the light phase can be divided :o a multiplicity of fractions by stagewise alteration of nperature or pressure. The supercritical solvent, sometimes hereinafter referred as the carrier gas is a polar uid preferably a gas ving a critical temperature which is at least 200 F. s than that of the asphalt. The polar solvent preferred is a nitrogen containing wis Base, an acid anhydride gas, acid gases such as 3l, HBr and HQS, or a low molecular weight organic lehyde, ether, alcohol, ketone or acid. The critical aperties of some of the polar solvents are set forth Mixtures of any-of the above solvents can be used the polar components of the supercritical gas. Typical supercritical separation conditions for use with petroleum asphalt are set forth below in Table 1I.

.una v11.--s'umtnonrfrrclsn SEPARATION CONDITIONS mperature Gradient, F

Referring to the drawing, dimethyl ether solvent is passed by line 16 into tower 15. A light extract phase comprising oil having an intermediate metals content of about 1GO-500 p.p.m. and solvent is recovered overhead by line 17. The light phase is passed through heater 18 into flash drum 19. The solvent is dashed overhead into linel 16. The solvent is cooled in coolerZt) and repressured by pump 21 for recycle to the SCS Unit. Make-up solvent is added by line 22. The intermediate metals oil is recovered by line 23. In a preferred embodiment a portion of the oil in line 23 is pumpedvia line 24 and pump 25 as reflux to the SCS Unit. In another preferred embodiment a portion of the oil is recycled by lines 23 and 26 to the inlet line 4 of the deasphalting tower for further treatment. Another portion of the oil, i.e. 25-90% is recovered from the process byline 27. This oil is a suitable fuel oil. High metals asphalt is recovered by line 28.

When the process of the invention is applied to typical Latin American feeds the following exemplary results will 4be obtained.

TABLE IIL-COMPOSITIONS AND YIELDS OR Table III. shows that only 10% of the crude oil is rejected as high metals asphalt. Supercritical separation thus provides an additional 1520% oil which can be blended with low metals oil, recycled to deasphaltingfor further metals reduction, or refined in suitable processes such as slurryhydro'desulfurization, coking, etc.

What is claimed is: i i

1. A process for the demetallization of a residuum fraction comprising the steps of (a) Contacting the residuum with a non-polar solvent at deasphalting conditions, l

(b) Recovering a low metals deasphalted oil extract,

(c) Contacting the asphalt with a polar solvent selected from the group consisting of ammonia, monomethyl amine, dimethyl amine, nitrous oxide, sulfur dioxide, methyl chloride, dimethyl ether, methyl alcohol, formaldehyde, acetone, HCl, -HBr and mixtures thereof at supercritical conditions in which the initial boiling point of the feed is about 200 F. above the critical temperature of the polar solvent,` and the pressure is above the critical pressure of the polar solvent, Y. A y

(d) Recovering an intermediate metalsextract of low` metals content, and f (e) Recovering a high'metals asphalt.

petroleum 2. Process according to claim 1 in whichsaid'residinrni'NV i fraction contains at least 100.p.p.m. metals; .L 3. A process for the'demetallization of a petroleum residuum fraction containing atleast p.p.m.metals" comprising the steps of (a) Countercurrently,contacting said lfeed in a `deasphalting zone with a process-solvent at a temperature inthe rangeof to 1959,11.,

(b) Recovering an extract phasev containing less than about 50 ppm. metals,

` 6 (c) Countercurrently contacting the raffinate from step 1 in a supercritical contacting zone with a polar References Cited solvent selected from the grdcltlilp t1coisisting ofularn- UNITED STATES PATENTS monia, monomethyl amine, e y amine, ni ous I oxide, sulfur dioxide, methyl chloride, dimethyl '5 afrsonal" ether, methyl alcohol, formaldehyde, acetone, HC1, 287g149 2/1959 a et 208 73 HBr and mixtures thereof at a (CI{) temperature ,2850 431 10/1958 s .n ""T' "208 "E09 of 5-50 F. above the critical temperature and a m1 (CP-H pressure of 30G-1000 p.s.i.g. above the FOREIGN PATENTS critical pressure, (d) Recovering an extract oil containing less than 500 1o 5661979 12/1958 Canada' p.p.m. metals, and (e) Blending the extract phases of steps 2 and 4. DELBERT E' GANTZ Primary Examiner 4. Process according to claim 3 in which the polar J- M- NELSON, Assistant EXamIler solvent is dimethyl ether. 15

5. Process according to claim 3 in which the polar U'S Cl' X-R- solvent is dimethyl amine. 208-86, 252, 309, 334 

